The present invention relates to the field of paper machine clothing, and more particularly to clothing for use in the dryer sections of such machines. The dryer section of a paper making machine is that portion of the machine wherein a wet paper web is dried down to about 6% water on large cast iron, steam-heated cylinders. These large smooth cylinders dry the web into a flat sheet. A dryer felt/fabric is needed to hold the wet web in intimate contact with the smooth dryers, otherwise wrinkles and cockles may develop in the sheet. If the sheet is not flat, serious difficulties may develop in the printing process. As paper machines have developed, dryer felts approaching 400 inches in width have come into use. Venting pockets in the dryers intended to purge excessive hot, moist air have also been developed which require new, extremely permeable dryer felt designs. Additionally, over the years the speed of operation of such dryer felts has increased, and is now approaching the four to five thousand feet per minute range. Since dryer felts are formed in the shape of long belts which are threaded around various guides, cylinders and rollers in almost all paper making machines, it is necessary to provide a seam in the felt at which the two ends, known as lap and hook ends, may be joined after the felt has been threaded. Due to the high speed, pressure, moisture, heat and other conditions of operation to which these dryer felts are subjected, the seam and the fabric in the immediate vicinity of the seam are subjected to extreme wear conditions. Additionally, substantially increased thickness in overlapped fabric ends can result in marking and/or other irregularities in the paper product to be dried.
In recent years, monofilament dryer fabrics have been developed which utilize "pin" seams wherein alternate monofilament warp ends are caused to form a "loop" at the end of the fabric and are woven back into the body of the fabric. The loops thus formed at the end of a monofilament fabric mate with complemental loops formed in the other end of that fabric so that a long wire or "pin" (pintel) may be inserted through the channel formed therebetween to join the two fabric ends. A seam thus formed in a monofilament fabric is not substantially thicker than the normal fabric thickness.
In recent years, various coil-type seams have also been developed wherein coils or spirals are inserted along a fold line. The fabric is folded back over itself and sewn or otherwise attached to itself to retain the coil and mateably receive a coil similarly attached to the other end of the dryer felt/fabric. A pin or wire may then be used to join the seam. To date, attempts to create a true "pin" type seam in multi-filament fabrics have been unsuccessful due to a lack of stability of the geometric configuration of loops formed from multi-filament (and even some monofilament) warp yarns of such fabric. While coil seams have achieved some success in the field of paper machine clothing, the additional thickness and thickness irregularity attendant with such seams has limited their applicability, life and/or reliability.
Various materials have been suggested for use in making coil-type seams. For example, spirals of polyester monofilament have been suggested which are manufactured by taking extruded polyester monofilament yarn, wrapping it around a mandrel, and heat setting it to cause it to take a spiral shape. It is also known to create spirals of multi-filament material, particularly materials which is capable of being heat set in a similar manner. For example, it is known to create a spiral or coil for insertion into a coil-type seam by taking a nylon monofilament and using a conventional braiding machine to braid around that monofilament with polyester and aramide threads. The resulting braided coil may be wound on a mandrel and heat set. As used hereinafter in this application, the term "coil material" shall refer to any of the spirals or coils heretofore known to the art, but preferably to the braided multi-filament coil described above.